Engine cooling device

ABSTRACT

The cooling device is provided with an ECU, a water pump, an engine, a water-cooled exhaust manifold, and a radiator. A first flow rate determination means that determines the flow rate of the cooling water allowed to flow through the water-cooled exhaust manifold based on the intake air flow rate when the operation state of the engine is in a steady state, and a second flow rate determination means that determines the flow rate of the cooling water allowed to flow through the water-cooled exhaust manifold based on the cooling loss when the operation state of the engine is in a transient state are functionally achieved by the ECU.

TECHNICAL FIELD

The present invention relates to an engine cooling device, and more particularly, relates to an engine cooling device provided with an exhaust system cooling means that cools an exhaust system of an engine with flowing coolant.

BACKGROUND ART

There has been conventionally known the art that cools an exhaust system of engine (more specifically, an exhaust manifold for example) with a coolant such as water. In regard to this art, a related art of the present invention is disclosed in Patent Document 1 for example. Patent Document 1 discloses an exhaust manifold device provided with a water jacket formed around an exhaust manifold, and a water injection means that sprays water to the water jacket. As another related art of the present invention, Patent Document 2 discloses a cooling control device of internal combustion engine provided with a flow rate control valve that can change the supply ratio of cooling medium to a number of cooling units. More specifically, Patent Document 2 discloses a cooling control device of internal combustion engine where flow rate control valves are provided to respective cooling water paths that guide cooling water to respective cooling units such as exhaust ports and the like.

-   [Patent Document 1] Japanese Patent Application Publication No.     63-208607 -   [Patent Document 2] Japanese Patent Application Publication No.     2007-132313

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

It is required to reduce the exhaust emission in the engine as an approach to environmental problems. In this point, when reducing the exhaust emission at the time of light/middle-load-driving mainly, there is a method of making the three-way catalyst located adjacent to the engine and warming up the three-way catalyst early.

On the other hand, it is desired to operate the engine at the theoretical air fuel ratio or the vicinity of the theoretical air fuel ratio to reduce the exhaust emission at the time of high-load driving with the above method. However, in this case, due to the location of the coolant adjacent to the engine, the coolant is overheated, and the excess progression of the deterioration and the degradation of the exhaust emission caused by the excess progression of the deterioration are concerned as a result. Therefore, considering the reduction of the exhaust emission in a high-load driving region, it is necessary that the three-way catalyst is located away from the engine. However, as there is a possibility that the reduction of the exhaust emission in the light/middle-load driving region where the catalyst is warmed up early becomes inadequate, it is necessary to increase the amount of the noble metals which promotes the purification of the catalyst. However, the noble metals are precious, and the increase of cost is concerned in this case.

Under this circumstances, it is considered to decrease the exhaust temperature by cooling the exhaust system with a coolant in order to achieve further reductions of the exhaust emission in the light/middle-load driving region where the catalyst is warmed up early and the exhaust emission at the high-load driving. This also makes it possible to suppress the overheat of the catalyst. Thus, this makes it possible to arrange the catalyst adjacent to the engine, and it becomes possible to achieve further reductions of the exhaust emission in the light/middle-load driving region where the catalyst is warmed up early and the exhaust emission at the high-load driving.

When cooling the exhaust system with a coolant as described above, it is reasonable to share the coolant flowing through the engine body (e.g. long life coolant which is cooling water of the engine) in terms of cost.

In addition, a coolant flowing through the engine body is generally pumped by the mechanical water pump which is driven by the output power of the engine. Therefore, when the coolant flowing through the engine body is shared, it is reasonable to use a mechanical water pump as the coolant pumping device in terms of cost.

However, there are following problems in this case. Here, it is necessary to maintain the coolant at a proper temperature even when cooling the exhaust system with the coolant shared with the engine body. At this point, a coolant flowing through the engine body is generally cooled by a cooling device (e.g. radiator). In addition, in regard to the coolant flowing through the engine body, the coolant temperature at the exit side of the engine body or at the flowing path just after flowing through the engine body is detected as the coolant temperature in the engine body (hereinafter, referred to as an engine coolant temperature).

Thus, in order to maintain the coolant at the proper temperature, it is considered to adjust the flow rate of the coolant flowing into the radiator based on the engine coolant temperature for example.

However, the engine coolant temperature described above does not represent a coolant temperature in the exhaust system cooling means (hereinafter, referred to as the exhaust system coolant temperature). More specifically, as illustrated in FIG. 21, there is a tendency that the exhaust system coolant temperature is normally greater than the engine coolant temperature. This is because the size of the exhaust system cooling means is normally smaller than that of the engine body, and the heat capacity of the exhaust system cooling means is smaller than that of the engine body. Therefore, in this case, there is a possibility that the coolant is overheated or boiled in the exhaust system cooling means. In other words, it is difficult to know the overheat or boiling of the coolant in the exhaust system cooling means from the engine coolant temperature.

It is considered to handle this point as follows for example. Here, from FIG. 21, in regard to the average temperature after warm-up, the engine coolant temperature is a certain degree higher than the exhaust system coolant temperature. Therefore, in regard to this point, it is considered that it is only necessary to set the engine coolant temperature to the one which is a certain degree higher than the temperature actually detected.

However, when pumping the coolant shared with the engine body to the exhaust system cooling means by a mechanical water pump, there are further following problems.

Here, the discharge rate of the mechanical water pump generally rises and falls in proportion to the rotation number of the engine. Therefore, when the operation state of the engine is high-rotation/high-load, the flow rate of the coolant in the exhaust system cooling means becomes large. On the other hand, as the intake air flow rate is large and the calorific value of the engine becomes large in this case, the received calorie value that the exhaust system cooling means receives from the exhaust gas increases. Therefore, in this case, the heat is kept in the wall that forms the flow path through which the exhaust gas flows, and the wall is heated to a high temperature as a result.

Assume that the operation state of engine moves from the operation state of high-rotation/high-load to the operation state of low-rotation/high-load after that. In this case, the temperature of the above-described wall is kept high for a while. However, on the other hand, in this case the flow rate of the coolant in the exhaust system cooling means decreases as the rotation number of engine decreases. Therefore, in this case, the received heat value from the exhaust gas exceeds the radiation amount by the coolant in the exhaust system cooling means. That is to say, in this case the flow rate of the coolant in the exhaust system cooling means runs temporarily short against the calorific value of the engine in this case.

Even though adjusting the flow rate of the coolant flowing into the radiator in response to the engine coolant temperature as described previously, it is not possible to handle the shortage of the flow rate of the coolant in the exhaust system cooling means. Therefore, in this case, even though the engine coolant temperature is set to be a certain degree higher than the temperature actually detected, there is a problem in that the coolant is overheated or boiled in the exhaust system cooling means.

The present invention was made in view of the above problems, and has an object of providing an engine cooling device capable of preventing or suppressing an overheat or boiling of a coolant in an exhaust system cooling means when the exhaust system cooling means that cools an exhaust system of the engine with the shared coolant flowing through an engine body is provided.

Means for Solving the Problems

The present invention to solve above problems is an engine cooling device including: a coolant pumping device that pumps a shared coolant to a plurality of coolant circulation paths; an engine of which an engine body is mounted in at least one of the plurality of coolant circulation paths; an exhaust system cooling means which is mounted in at least one of the plurality of coolant circulation paths, of which a heat capacity is smaller than that of the engine body, and which cools an exhaust system of the engine by a flowing coolant; a cooling device that is mounted in at least one of the plurality of coolant circulation paths, and cools a flowing coolant; and a flow rate determination means that determines a flow rate of a coolant allowed to flow through the exhaust system cooling means based on an intake air flow rate of the engine.

In addition, the present invention is an engine cooling device including: a coolant pumping device that pumps a shared coolant to a plurality of coolant circulation paths; an engine of which an engine body is mounted in at least one of the plurality of coolant circulation paths; an exhaust system cooling means which is mounted in at least one of the plurality of coolant circulation paths and cools an exhaust system of the engine by a flowing coolant, and of which a heat capacity is smaller than that of the engine body; a cooling device that is mounted in at least one of the plurality of coolant circulation paths and cools a flowing coolant; and a flow rate determination means that determines a flow rate of a coolant allowed to flow through the exhaust system cooling means based on a received heat amount that a coolant receives from an exhaust in the exhaust system cooling means.

In addition, it is preferable that the present invention has a configuration further including: an estimation means that estimates a temperature of a wall, which forms a flow path through which an exhaust gas flows, of the exhaust system cooling means; and a correction means that corrects a flow rate of a coolant determined by the flow rate determination means based on the estimation.

Effects of the Invention

According to the present invention, it is possible to prevent or suppress the overheat or boiling of a coolant in the exhaust system cooling means when the exhaust system cooling means that cools an exhaust system of an engine with a shared coolant flowing through the engine body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating an engine cooling device (hereinafter, referred to as a cooling device) 100A in accordance with a first embodiment, where pipes forming a cooling water circulation path at a cooling time when a valve of a thermostat 60 is closed are illustrated by dashed lines, pipes forming a cooling water circulation path at a warming time when the valve of the thermostat 60 is opened are illustrated with solid lines, and a flowing direction of cooling water W is illustrated by arrows (this is also applied to FIG. 5 through FIG. 10);

FIG. 2 is a diagram schematically illustrating a water-cooled exhaust manifold 30;

FIG. 3 is a diagram illustrating flow characteristics of cooling water W flowing through the water-cooled exhaust manifold 30;

FIG. 4 is a diagram schematically illustrating a flow rate changing structure 70, where the dashed line illustrates a state where an idler pulley 74 pushes a belt 73 from a state illustrated with solid lines;

FIG. 5 is a diagram illustrating a first cooling water circulation path 81;

FIG. 6 is a diagram illustrating a second cooling water circulation path 82;

FIG. 7 is a diagram illustrating a third cooling water circulation path 83;

FIG. 8 is a diagram illustrating a fourth cooling water circulation path 84;

FIG. 9 is a diagram illustrating a fifth cooling water circulation path 85;

FIG. 10 is a diagram illustrating a sixth cooling water circulation path 86;

FIG. 11 is a diagram schematically illustrating a practical configuration of an ECU (Electronic Control Unit) 1A;

FIG. 12 is a diagram illustrating relationship between (ethw+etha)×NE/100×GA and an actual cooling loss Qw, where R² is a value indicating a degree of correlation, and the degree of correlation becomes high as R² is closer to 1 (this is also applied to FIG. 14);

FIG. 13 is a diagram illustrating an operation of the ECU 1A with a flowchart;

FIG. 14 is a diagram illustrating a relationship between the intake air flow rate GA and the actual cooling loss Qw;

FIG. 15 is a diagram schematically illustrating a map data of flow rate correction amount set according to an accumulated amount of intake air flow rate ΣGA;

FIG. 16 is a flowchart illustrating an operation of an ECU 1B;

FIG. 17 illustrates a timing chart according to the operation of the ECU 1B;

FIG. 18 is a timing chart to explain the concept of the flow rate control by the ECU 1B, where the solid line indicates a case where the operation state of the engine 20 moves from the high-rotation/high-load operation state to the low-rotation/non-high-load operation state, and the dashed line indicates a case where the operation state of the engine 20 moves from the high-rotation/high-load operation state to the low-rotation/high-load operation state;

FIG. 19 is a diagram unifying results of measurements of the water temperature inside the water-cooled exhaust manifold 30 and the observation of the cooling water W inside the water-cooled exhaust manifold 30 according to the intake air flow rate GA by visualization by providing the window to the water-cooled exhaust manifold 30;

FIG. 20 is a diagram schematically illustrating a variable water pump pulley 76 and a belt 73B, more specifically, FIG. 20( a) illustrates the pulley 76 in a state where each pulley member 76 a contacts thereto, and FIG. 20( b) illustrates the pulley 76 in a state where pulley members 76 a are apart from each other; and

FIG. 21 is a diagram illustrating changes of the engine coolant temperature and the exhaust system coolant temperature after starting the cooling of the engine, together with the vehicle speed, the rotation number of engine and a throttle opening degree.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a detail description will be given of modes for carrying out the present invention with reference to drawings.

First Embodiment

A description will be given of a cooling device 100A with reference to FIG. 1 through FIG. 11. As illustrated in FIG. 1, the cooling device 100A is provided with an ECU 1A, a water pump 10, an engine 20, a water-cooled exhaust manifold 30, a heater core 40, a radiator 50, and a thermostat 60. The water pump 10 is mounted in the engine 20. The water pump 10 is a mechanical pump driven by the output power of the engine 20, and pumps the cooling water W which is a coolant. The discharge rate of the water pump 10 rises and falls in proportion to the rotation number NE of the engine 20.

The engine 20 includes an engine body 21. The engine body 21 is composed of cylinder heads and cylinder blocks not illustrated. A water jacket 22, a bypass path 23, and a communication path 24 are formed in the engine body 21. The cooling water W flows through the water jacket 22, and the cooling water W flowing through the water jacket 22 cools the engine body 21. The bypass path 23 flows the cooling water W from the water jacket 22 to the thermostat 60. The bypass path 23 connects the exit of the water jacket 22 and the outside of it. The communication path 24 connects the entrance of the bypass path 23 and the outside of it. The engine body 21 is provided with a water temperature sensor 91 that detects a cooling water temperature THW which is the temperature of the cooling water W, and an engine rotation number sensor 92 used to detects a rotation number NE of the engine 20. The water temperature sensor 91 is located so as to detect the cooling water temperature THW at the exit of the water jacket 22.

The water-cooled exhaust manifold 30 is mounted in the engine body 21. The water-cooled exhaust manifold 30 merges exhaust gasses exhausted from cylinders of the engine 20. As illustrated in FIG. 2, the water-cooled exhaust manifold 30 includes an external wall 302 that wholly houses exhaust pipes 301. The external wall 302 forms cooling water flow paths between exhaust pipes 301 and the external wall 302. In the water-cooled exhaust manifold 30, while the cooling water W is supplied to the cooling water flow path from a cooling water inlet 303, the cooling water W is discharged from the cooling water flow path via cooling water outlets 304. The flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 increases or decreases in proportion to the rotation number NE of the engine 20 (see FIG. 3). In this embodiment, the water-cooled exhaust manifold 30 corresponds to the exhaust system cooling means, and exhaust pipes 301 correspond to a wall that forms a flow path through which the exhaust gas flows.

Back to FIG. 1, the heater core 40 executes a heat transfer between the cooling water W and the air. The heater core 40 is utilized in an air-conditioning unit not illustrated. The air-conditioning unit functions as a heating apparatus by sending the air warmed by the heater core 40 into the vehicle interior of the car. The radiator 50 promotes the heat release from the flowing cooling water W by the traveling wind or the wind from the electric fan not illustrated, and cools the cooling water W. In this embodiment, the radiator 50 corresponds to a cooling device. The thermostat 60 operates so as to control the flow of the cooling water W by closing a valve during cooling and by opening a valve during warming.

The cooling device 100A is provided with the flow rate changing structure 70 illustrated in FIG. 4. The flow rate changing structure 70 enables the control of the rotation number of the water pump 10 according to the intake air flow rate GA, the load factor of the engine 20, and the pressure of the intake pipe for example. The flow rate changing structure 70 changes the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 by enabling the control of the rotation number of the water pump 10. The flow rate changing structure 70 is provided with a crank pulley 71, a water pump pulley 72, a belt 73, an idler pulley 74, and an actuator 75.

The pulley 71 is linked to a crankshaft of the engine 20 not illustrated.

The pulley 72 is linked to a rotating shaft of the water pump 10. The pulley 72 has a frustum shape, and its diameter is gradually reduced from one end to another end in an axial direction.

The belt 73 has a ring shape, and is looped around pulleys 71 and 72. A home position of the belt 73 on the pulley 72 is a one-end side.

The pulley 74 is provided so as to contact with the belt 73 between pulleys 71 and 72. The pulley 74 is connected to the actuator 75. The actuator 75 is provided so as to drive the pulley 74 along a direction in which the belt 73 can be pressed. A stepping motor to which a direct acting mechanism is combined can be used as the actuator 75. The operation of the flow rate changing structure 70 is as follows. During the operation of the engine 20, the pulley 71 rotates in conjunction with the crankshaft. The rotation of the pulley 71 is transmitted to the pulley 72 via the belt 73. Then, when the pulley 72 rotates, the water pump 10 is driven accordingly. At this time, the water pump 10 pumps the cooling water W at the discharge rate according to the rotation number NE.

On the other hand, when the actuator 75 drives the pulley 74, and presses the pulley 74 against the belt 73, the tension of the belt 73 increases. In addition, as illustrated with dashed lines when the belt 73 is pushed by the pulley 74, the belt 73 slides from the one-end side to the other-end side of which the diameter is smaller on the pulley 72. According to this, the diameter of the pulley 72 corresponding to the belt 73 is reduced. Therefore, the rotation of the water pump 10 is increased, and the discharge rate is increased. The discharge rate of the water pump 10 may be decreased by operating the actuator 75 inversely.

The cooling device 100A includes first through sixth cooling water circulation paths 81 through 86 corresponding to a plurality of cooling water circulation paths as illustrated in FIG. 5 through FIG. 10. First, second and third cooling water circulation paths 81, 82 and 83 are circulation paths where the flow of the cooling water W is allowed when the thermostat 60 closes. Fourth, fifth and sixth cooling water circulation paths 84, 85 and 86 are circulation paths where the flow of the cooling water W is allowed when the thermostat 60 opens. More particularly, the water pump 10 pumps the cooling water W shared in these cooling water circulation paths 81 through 86. In this embodiment, the water pump 10 corresponds to a coolant pumping device.

One of the water pump 10, the engine 20, the water-cooled exhaust manifold 30, the heater core 40, the radiator 50 and the thermostat 60 is arbitrarily mounted in cooling water circulation paths 81 through 86. In cooling water circulation paths 81 through 86, these components are coupled each other directly or via a pipe. A description will now be given of cooling water circulation paths 81 through 86 more specifically.

Specifically, the first cooling water circulation path 81 is a circulation path through which the cooling water W flows in order of the water pump 10, the engine body 21, the heater core 40, and the thermostat 60 that are mounted therein. In addition, when the cooling water W flows through the engine body 21, it specifically flows through the water jacket 22.

The second cooling water circulation path 82 is particularly a circulation path through which the cooling water W flows in order of the water pump 10, the engine body 21 and the thermostat 60 that are mounted therein. In addition, when the cooling water W flows through the engine body 21, it flows through the water jacket 22 and the bypass path 23 in this order particularly.

The third cooling water circulation path 83 is a circulation path through which the cooling water W flows in order of the water pump 10, the water-cooled exhaust manifold 30, the engine body 21, and the thermostat 60 that are mounted therein. When the cooling water W flows through the engine body 21, it flows through the communication path 24 and the bypass path 23 in this order particularly.

First through third cooling water flow paths 81 through 83 are circulation paths not including the radiator 50.

The fourth cooling water circulation path 84 is particularly a circulation path through which the cooling water W flows in order of the water pump 10, the engine body 21, the heater core 40, and the thermostat 60 that are mounted therein. In addition, when the cooling water W flows through the engine body 21, the cooling water W flows through the water jacket 22.

The fifth cooling water circulation path 85 is particularly a circulation path through which the cooling water W flows in order of the water pump 10, the engine body 21, the radiator 50, and the thermostat 60 that are mounted therein. In addition, when the cooling water W flows through the engine body 21, it flows through the water jacket 22 particularly.

The sixth cooling water circulation path 86 is particularly a circulation path through which the cooling water W in order of the water pump 10, the water-cooled exhaust manifold 30, the radiator 50, and the thermostat 60 are mounted therein,

In cooling water circulation paths 81 through 86 configured as described above, the cooling water W flows through the water-cooled exhaust manifold 30 when the thermostat 60 opens and closes. Therefore, the flow rate changing structure 70 can arbitrarily change the flow rate of the cooling water W flowing into the water-cooled exhaust manifold 30 during the opening and closing of the thermostat 60 (i.e. during the operation of the engine 20).

As illustrated in FIG. 11, the ECU 1A is provided with a microcomputer composed of a CPU 2, a ROM 3, a RAM 4 and the like, and input/output circuits 5 and 6. The CPU 2, the ROM 3, the RAM 4, and input/output circuits 5 and 6 are coupled each other via a bus 7. The ECU 1A is configured to control the engine 20 mainly. More particularly, the ECU 1A is configured to control the fuel injection valve not illustrated for example. In addition, the ECU 1A is configured to control the actuator 75 in addition to this. These controlled objects are electrically coupled to the ECU 1A.

Various sensors, such as the water temperature sensor 91, the engine rotation number sensor 91, an air flow meter 93 (more particularly, an intake air flow rate sensor 93 a and an intake air temperature sensor 93 b), and the throttle opening degree sensor 94, are electrically coupled to the ECU 1A. The cooling water temperature THW is detected based on the output of the water temperature sensor 91, the rotation number NE is detected based on the output of the engine rotation number sensor 92, the intake air flow rate GA and the intake air temperature THA of the engine 20 are detected based on the output of the air flow meter 93, and the opening degree TA of the throttle valve adjusting the intake air flow rate GA (its illustration is omitted) is detected based on the output of the throttle opening degree sensor 94 in the ECU 1A.

The ROM 3 is a component to store programs where various processes executed by the CPU 2 are written and map data. A control means, a determination means, a detection means, and a calculation means are functionally achieved in the ECU 1A by the execution of the process by the CPU 2 based on programs stored in the ROM 3 with using a temporary memory region of the RAM 4 as needed.

From this point, in the ECU 1A, a detection means detecting estimation factors including the intake air flow rate GA of the engine 20 for example, and an estimation means estimating a cooling loss Qw which is a received heat quantity that a coolant receives from the exhaust in the water-cooled exhaust manifold 30 based on estimation factors detected by the detection means (hereinafter, abbreviated as a cooling loss estimation means) are functionally achieved.

The reason why the above-described estimation factors include the intake air flow rate GA is because the intake air flow rate GA has a high linear correlation with the cooling loss Qw.

It is preferable that the above-described estimation factors further include at least one of the cooling water temperature THW which is a coolant temperature, the intake air temperature THA, and the rotation number NE. This is because these four factors are factors having a great effect on the cooling loss Qw.

More specifically, if the operation environment condition of the engine 20 such as initial state changes, the cooling loss Qw also changes. The cooling water temperature THW and the intake air temperature THA can represent the operation environment condition of the engine 20. In addition, when the friction of the engine 20 increases, as the heat quantity evolved from the engine 20 increases, the cooling loss Qw tends to increase. The rotation number NE can represent a magnitude of the friction of the engine 20. Therefore, when estimating the cooling loss Qw more accurately, it is preferable that at least one of the cooling water temperature THW, the intake air temperature THA, and the rotation number NE is further included.

Furthermore, it is most desirable to estimate the cooling loss Qw based on a following formula (1) which includes all the four factors.

Qw=(THW+THA)×NE×GA   formula (1)

That is to say, it is most desirable to estimate the cooling loss Qw based on the value calculated by multiplying the sum of the cooling water temperature THW and the intake air temperature THA by the rotation number NE and the intake air flow rate GA. This is because the highest-linear correlation with the actual cooling loss Qw is revealed when estimating the cooling loss Qw based on the formula (1) from the result of a bench test of the engine 20 which includes a steady state and a transient state as an operation state (see FIG. 12). Therefore, in the ECU 1A, the cooling loss Qw is specifically estimated based on the formula (1).

In addition, in the ECU 1A, a means that determines whether an operation state of the engine 20 is in a steady state or in a transient state based on the change of opening degree of the throttle valve ΔTA is functionally achieved as a determination means that determines an operation state of the engine 20 (hereinafter, referred to as a first operation state determination means). More specifically, the first operation state determination means determines that the operation state is in a steady state when the change of opening degree ΔTA is equal to or smaller than a given value, and determines that the operation state is in a transient state when the change of opening degree ΔTA is smaller than a given value.

In addition, in the ECU 1A, a determination unit that determines the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 based on the intake air flow rate GA (hereinafter, referred to as a first flow rate determination means) is functionally achieved. More specifically, the first flow rate determination means determines the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 based on the intake air flow rate GA when the operation state of the engine 20 is in a steady state in this embodiment.

Furthermore, in the ECU 1A, a determination means that determines the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 based on the cooling loss Qw (hereinafter, referred to as a second flow rate determination means) is functionally achieved. More specifically, the second flow rate determination means determines the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 based on the cooling loss Qw estimated by the cooling loss estimation means when the operation state of the engine 20 is in a transient state.

In addition, in the ECU 1A, a control means that controls the flow rate of the cooling water W (hereinafter, referred to as a flow rate control means) is functionally achieved. More specifically, the flow rate control means handles the flow rate changing structure 70 (more specifically, the actuator 75) as a controlled object, and controls the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 to be the flow rate determined by the first or second flow rate determination means. The flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 is determined and controlled simultaneously by determining and controlling the discharge rate of the water pump 10.

A description will now be given of an operation of the ECU 1A by using a flowchart illustrated in FIG. 13. The flowchart is executed repeatedly at a very short time interval during the operation of the engine 20. The ECU 1A detects the throttle opening degree TA, and calculates the change of the throttle opening degree ΔTA (step S1). Then, the ECU 1A determines whether the calculated change of opening degree ΔTA is equal to or smaller than a given value (step S2). When the determination result is Yes in the step S2, the operation state of the engine 20 is determined to be a steady state. At this time, the ECU 1A detects the intake air flow rate GA (step S3).

Then, the ECU 1A determines the discharge rate of the water pump 10 based on the detected intake air flow rate GA (step S4). More specifically, the ECU 1A determines the discharge rate of the water pump 10 based on the cooling water flow characteristics according to the intake air flow rate GA (hereinafter, referred to as a first flow characteristic of cooling water) at this time. Then, the ECU 1A controls the actuator 75, and changes the discharge rate of the water pump 10 to the determined discharge rate (step S8). After the step S8, this flowchart is ended.

On the other hand, when the determination result is No in the step S2, the operation state of the engine 20 is determined to be a transient state. At this time, the ECU 1A detects the cooling water temperature THW, the intake air temperature THA, the rotation number NE, and the intake air flow rate GA (step S5). Then, the ECU 1A calculates (estimates) the cooling loss Qw based on the formula (1) (step S6). In addition, the ECU 1A determines the discharge rate of the water pump 10 based on the calculated cooling loss Qw (step S7). More specifically, the ECU 1A determines the discharge rate of the water pump 10 based on the cooling water flow characteristics according to the cooling loss Qw (hereinafter, referred to as a second flow characteristic of cooling water) at this time. After the step S7, the process goes to the step S8.

The above-described first flow characteristic of cooling water is defined by map data stored in the ROM 3 in advance. In this map data, the discharge rate of the water pump 10 is set to increase and decrease in proportion to the intake air flow rate GA. Accordingly, the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 is set to increase and decrease in proportion to the intake air flow rate GA.

In the same manner, the above-described second flow characteristic of cooling water is defined in map data stored in the ROM 3 in advance. In this map data, the discharge rate of the water pump 10 is set to increase and decrease in proportion to the cooling loss Qw. Accordingly, the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 is set to increase and decrease in proportion to the cooling loss Qw.

First and second flow characteristics of cooling water are prepared with respect to each of cooling time and warming time when the flow mode of the cooling water W is switched from cooling water circulation paths 81 to 86 for example. According to this, even though the flow mode of the cooling water W is switched, a flow rate control can be executed in the flow rate changing structure 70 more properly.

A description will be given of a function effect of the cooling device 100A. Here, it is considered to increase or decrease the flow rate in proportion to the rotation number NE for example when changing the flow rate of the cooling water W to prevent or suppress the overheat of the cooling water W in the water-cooled exhaust manifold 30. However, in a case where the operation state of the engine 20 is in a steady state, the intake air flow rate GA has a very high-linear correlation with the actual cooling loss Qw (see FIG. 14). In addition, from the aspect of the calorific value of the engine 20, it is desirable that the cooling water flow characteristic is a characteristic capable of increasing and decreasing the flow rate of the cooling water W in proportion to the intake air flow rate GA which is almost equal to the exhaust gas amount.

On the other hand, in the cooling device 100A, the ECU 1A determines and changes the discharge rate of the water pump 10 (in other words, the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30) based on the first flow characteristic of cooling water at a steady time. That is to say, in the cooling device 100A, regardless of the rotation number NE and the exhaust temperature, it is possible to increase the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 properly as the calorific value becomes larger, in accordance with the calorific value of the engine 20. Therefore, the cooling device 100A can prevent or suppress the overheat or boiling of the cooling water W in the water-cooled exhaust manifold 30 at a steady time. More specifically, according to this, it is possible to prevent or suppress a decrease in cooling efficiency of the exhaust gas of the water-cooled exhaust manifold 30, a decrease in durability or reliability of the water-cooled exhaust manifold 30 caused by thermal strain, and a deterioration of the cooling water W for example.

On the other hand, when the operation state of the engine 20 is in a transient state, the fluctuation of ignition timing and a difference of the operation state before the transition to a transient state affect on the calorific value of the engine 20. The cooling loss Qw based on the formula (1) has a high-linear correlation with the actual cooling loss Qw at a transient time as illustrated in FIG. 12. In addition, in the cooling device 100A, the ECU 1A determines and changes the discharge rate of the water pump 10 (in other words, the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30) based on the second flow characteristic of cooling water at a transient time. That is to say, in the cooling device 100A, it is possible to increase the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 properly as the calorific value becomes larger, in accordance with the calorific value of the engine 20 in a transient state. Therefore, the cooling device 100A can prevent or suppress the overheat or boiling of the cooling water W in the water-cooled exhaust manifold 30 also at a transient time.

In addition, the cooling device 100A includes the flow rate changing structure 70. Thus, the cooling device 100A can change the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 even when pumping the cooling water W by the mechanical water pump 10.

In order to prevent or suppress the overheat of the cooling water W in the water-cooled exhaust manifold 30 at the transient time, it is considered to set the flow rate of the cooling water W to match the maximum calorific value of the engine 20 for example. However, in this case, the flow rate of the cooling water W becomes unnecessarily large at the transient time when the calorific value is relatively small. Therefore, in this case, the water-cooled exhaust manifold 30 results in a supercooled state, and this may have a bad effect on the fuel consumption of the engine 20 and the durability and reliability of the water-cooled exhaust manifold 30. On the other hand, in the cooling device 100A, the ECU 1A changes the flow rate of the cooling water W according to the calorific value of the engine 20 in a transient state. Thus, the cooling device 100A can prevent or suppress the fall of the water-cooled exhaust manifold 30 into the supercooled state.

Second Embodiment

A cooling device 100B in accordance with the present embodiment is substantially same as the cooling device 100A except that it includes an ECU 1B instead of the ECU 1A. The ECU 1B is substantially same as the ECU 1A except that a determination means, an estimation means, and a correction means described later are further achieved functionally. Therefore, in this embodiment, the illustration of the cooling device 100B and the ECU 1B is omitted.

In the ECU 1B, a means that determines whether the operation state of the engine 20 is high-rotation/high-load (hereinafter, referred to as a second operation state determination means) is functionally achieved as a determination means that determines the operation state of the engine 20. More specifically, the second operation state determination means determines that the operation state is high-rotation/high-load when the intake air flow rate GA is equal to or greater than a given value, and determines that the operation state is not high-rotation/high-load when the intake air flow rate GA is smaller than a given value.

In addition, in the ECU 1B, an estimation means that estimates a temperature of the wall (more specifically, exhaust pipes 301) of the water-cooled exhaust manifold 30 forming the path through which the exhaust gas flows (hereinafter, referred to as a wall temperature estimation means) is functionally achieved. More specifically, in the present embodiment, the wall temperature estimation means estimates that the temperature of the wall is high when the operation state of the engine 20 is high-rotation/high-load.

In addition, a correction means (hereinafter, referred to as a flow rate correction means) that corrects the discharge rate of the water pump 10 determined by one of first and second flow rate determination means in accordance with the operation state of the engine 20 in the ECU 1B based on the estimation by the wall temperature estimation means, is functionally achieved. At this point, the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 is corrected simultaneously by correcting the discharge rate of the water pump 10.

The flow rate correction means is achieved as described hereinafter particularly. That is to say, the flow rate correction means calculates the accumulated amount of intake air flow rate ΣGA by accumulating the intake air flow rate GA when the temperature of the wall is high. Then, the flow rate correction means adds the flow rate correction amount based on the calculated accumulated amount of intake air flow rate ΣGA to the discharge rate of the water pump 10 which is set in one of first and second flow characteristics of cooling water in accordance with the operation state of the engine 20.

In addition, when the temperature of the wall becomes a less high temperature, the flow rate correction means updates the accumulated amount of intake air flow rate ΣGA by subtracting the current intake air flow rate GA from the accumulated amount of intake air flow rate ΣGA. Then, when the updated accumulated amount of intake air flow rate ΣGA is equal to or greater than a given value (e.g. 0), the flow rate correction means adds the flow rate correction amount according to the accumulated amount of intake air flow rate ΣGA to the flow rate of the cooling water W which is set in one of first and second flow characteristics of cooling water in accordance with the operation state of the engine 20.

More specifically, the flow rate correction amount is set to increase or decrease in proportion to the accumulated amount of intake air flow rate ΣGA in a high-load region in map data stored in the ROM 3 in advance as illustrated in FIG. 15.

A description will now be given of an operation of the ECU 1B by using a flowchart illustrated in FIG. 16 with reference to a timing chart illustrated in FIG. 17. As illustrated in FIG. 16, the ECU 1B detects the intake air flow rate GA (step S11). Then, the ECU 1B determines whether the detected intake air flow rate GA is equal to or greater than a given value which is a determination threshold value for the high-load determination (step S12). When the determination result is Yes in the step S12, the operation state of the engine 20 is determined to be high-rotation/high-load. When the determination result is Yes in the step S12, it is estimated that the temperature of the wall is high. At this time, the ECU 1B turns the high-load determination flag to ON (step S13). In FIG. 17, the state at the time T1 corresponds to this state.

Then, the ECU 1B accumulates the detected intake air flow rate GA, and calculates the accumulated amount of intake air flow rate ΣGA (step 14). Furthermore, the ECU 1B adds the flow rate correction amount according to the accumulated amount of intake air flow rate ΣGA to the discharge rate of the water pump 10 set in one of first and second flow characteristics of cooling water in accordance with the operation state of the engine 20 (step S15). After the step S15, this flowchart is ended. Then, the ECU 1B executes procedures from steps S11 through S15 repeatedly till the determination result becomes No in the step S12.

On the other hand, when the determination result is No in the step S12, the operation state of the engine 20 is determined not to be high-rotation/high-load. When the determination result is No in the step S12, it is determined that the temperature of the wall is not high. At this time, the ECU 1B turns the high-load determination flag to OFF (step S16). In FIG. 17, the state at the time T2 corresponds to above-described state. Then, the ECU 1B subtracts the current intake air flow rate GA from the accumulated amount of intake air flow rate ΣGA, and updates the accumulated amount of intake air flow rate ΣGA (step S17). Furthermore, the ECU 1B determines whether the calculated accumulated amount of intake air flow rate ΣGA is equal to or greater than a given value (here, 0) (step S18).

When the determination result is Yes in the step S18, the process goes to the step S15. Then, the ECU 1B executes above-described procedures repeatedly till the determination result becomes No in the step S18. On the other hand, when the determination result is Yes in the step S18, the ECU 1B resets the accumulated amount of intake air flow rate ΣGA (step S19). In FIG. 17, a state at the time T3 corresponds to this state. According to a sequence of above operations, the amount corresponding to the area of the accumulated amount of intake air flow rate ΣGA illustrated is added to the flow rate correction amount.

A description will now be given of a function effect of the cooling device 100B. Here, assume that the operation state of the engine 20 changes from an operation state of high-rotation/high-load to an operation state of low-rotation. In this case, as illustrated in FIG. 18, the rotation number NE decreases, and the intake air flow rate GA (i.e. the calorific value of the engine 20) decreases. However, the wall of the water-cooled exhaust manifold 30 stores a heat because of the reception of heat from the exhaust gas at high-rotation/high-load time. Especially, when the operation state of the engine 20 changes from an operation state of high-rotation/high-load to an operation state of low-rotation/high-load, the temperature of the wall of the water-cooled exhaust manifold 30 remains high for a certain period as illustrated in FIG. 18 with a dashed line.

On the other hand, in this case, the cooling capacity of the water-cooled exhaust manifold 30 decreases because the flow rate of the cooling water W decreases as the rotation number NE decreases. Therefore, in this case, the flow rate determined based on the intake air flow rate GA and the cooling loss Qw is not enough for cooling, and there is a possibility of the overheat or boiling of the cooling water W in the water-cooled exhaust manifold 30. More specifically, as illustrated in FIG. 19, the temperature of the cooling water W becomes high, and there is a possibility that the state where the boiling is locally recognized is achieved. In this case, a decrease in cooling efficiency of the exhaust gas of the water-cooled exhaust manifold 30 in a boiling portion, a decrease in durability or reliability of the water-cooled exhaust manifold 30 caused by the occurrence of the thermal strain because of temperature difference of parts, and deterioration of the boiled cooling water W occur for example.

On the other hand, in the cooling device 100B, the ECU 1B adds the flow rate correction amount based on the accumulated amount of intake air flow rate ΣGA to the discharge rate of the water pump 10 which is set in one of first and second flow characteristics of cooling water in accordance with the operation state of the engine 20. According to this, the flow rate of the cooling water W flowing through the water-cooled exhaust manifold 30 is further increased. Therefore, it is possible to cool the wall of the water-cooled exhaust manifold 30 which remains to have a high temperature for a certain period properly. Thus, the cooling device 100B can prevent or suppress the overheat or boiling of the cooling water W in the water-cooled exhaust manifold 30 even when the operation state of the engine 20 further moves from an operating state of high-rotation/high-load to an operation state of low-rotation/high-load.

Above-described embodiments are examples of preferred embodiments of the present invention. However, the present invention is not limited to these specifically described embodiments but may have various variations and alterations within the scope of the claimed invention.

For example, in above-described embodiment, a description was given of a case where the flow rate changing structure 70 is provided as the flow rate change means. However, the present invention is not limited to this case, and the flow rate change means may be other structures capable of changing the flow rate of the coolant.

At this point, more specifically, the flow rate change means can be achieved by the variable water pump pulley 76 illustrated in FIG. 20. This pulley 76 can be applied instead of the pulley 72. In this case, the idler pulley 74 is utilized to adjust the tension of the belt 73, and the actuator 75 becomes unnecessary.

The pulley 76 includes a pair of pulley members 76 a with a circular truncated cone shape. The pulley 76 includes a structure which can drive pulley members 76 a to move away from or come close to each other around the center in the axis direction. The belt 73 is looped around the pulley 76 so that it is looped around each pulley member 76 a equally. The pulley 76 is hydraulically-actuated, is applied as the controlled object instead of the actuator 75, and is able to drive each pulley member 76 a by switching the hydraulic pressure under the control of the ECU 1A.

The home position of each pulley member 76 a is a position where the pulley members 76 a contact with each other as illustrated in FIG. 20( a). When pulley members 76 a are driven to the direction moving away from each other as illustrated in FIG. 20( b), the diameter of the belt 73 is reduced on the pulley 76. Therefore, according to this, the rotation of the water pump 10 is increased, and the discharge rate can be increased. In addition, the discharge rate of the water pump 10 can be decreased by operating the pulley 76 inversely. In addition, it is possible to change the flow rate of the cooling water W when pumping the cooling water W by the mechanical water pump 10 by including the pulley 76 as the flow rate change means.

In addition, in above-described embodiments, a description was given of a case where the first flow rate determination means determines the flow rate at the steady time, and the second flow rate determination means determines the flow rate at the transient time because this is preferable in that the correlation with the actual cooling loss Qw is high and the flow rate control can be carried out more properly.

However, the present invention is not limited to this case, the flow rate determination means may be one of the first flow rate determination means and the second flow rate determination means at both the steady time and the transient time. In this case, the control can be simplified. In addition, in this case, when the steady time and the transient time are repeated in a relatively short period, it is possible to prevent the flow rate from being changed at different levels repeatedly by the first flow rate determination means and the second flow rate determination means, and to increase the reliability of the flow rate change means and to achieve the stabilization of the control.

In addition, in the present embodiment, the first flow rate determination means may determine a flow rate at least at a steady time, and the second flow rate determination means may determine the flow rate at least at a transient time.

Moreover, when one of first and second flow rate determination means determines the flow rate at a steady time and a transient time, the second flow rate determination means, which determines a flow rate based on the received heat quantity of the exhaust system cooling means, is preferable because the control of flow rate is carried out more properly as a whole.

Moreover, when one of first and second flow rate determination means determines the flow rate at a steady time and a transient time, the correction means may correct the flow rate determined by the flow rate determination means.

Furthermore, even in a case where the first flow rate determination means determines the flow rate at a steady time and the second flow rate determination means determines the flow rate at a transient time, one of first and second flow rate determination means (e.g. the second flow rate determination means) may determine the flow rate when the correction means corrects the flow rate. In this case, it is possible to improve the reliability of the flow rate change means and stabilize the control.

As above-described embodiments are preferable to be applied in a case where the coolant pumping device is the mechanical water pump 10, a description was given of this case. However, the present invention is not limited to this case, and it is possible to prevent or suppress the overheat or boiling of the coolant in the exhaust cooling means by applying the present invention even in a case where the coolant pumping device is an electric water pump.

In addition, in above-described embodiments, a description was given of a case where the exhaust system cooling means is the water-cooled exhaust manifold 30. However, the present invention is not limited to this case, and the exhaust system cooling means may be other arbitrary structures capable of cooling the engine exhaust system by a flowing coolant. The exhaust system cooling means may be achieved by an adapter that is located between the exhaust manifold and the engine for example and connects them.

In addition, it is reasonable to achieve each means such as the flow rate determination means, the estimation means, and the correction means by the ECU 1 that mainly controls the engine 20, but they may be achieved by one or combination of other electronic control devices and hardware such as a dedicated circuit. Each means such as the flow rate determination means, the estimation means and the correction means may be achieved by electronic control devices, hardware such as electronic circuits, or the combination of an electronic control devices and hardware such as an electronic circuit for example in a distributed manner. 

1. An engine cooling device comprising: a coolant pumping device that pumps a shared coolant to a plurality of coolant circulation paths; an engine of which an engine body is mounted in at least one of the plurality of coolant circulation paths; an exhaust system cooling unit which is mounted in at least one of the plurality of coolant circulation paths, of which a heat capacity is smaller than that of the engine body, and which cools an exhaust system of the engine by a flowing coolant; a cooling device that is mounted in at least one of the plurality of coolant circulation paths, and cools a flowing coolant; and a flow rate determination unit that estimates a cooling loss of an exhaust system based on an intake air flow rate of the engine, and determines a flow rate of a coolant allowed to flow through the exhaust system cooling unit.
 2. An engine cooling device comprising: a coolant pumping device that pumps a shared coolant to a plurality of coolant circulation paths; an engine of which an engine body is mounted in at least one of the plurality of coolant circulation paths; an exhaust system cooling unit which is mounted in at least one of the plurality of coolant circulation paths and cools an exhaust system of the engine by a flowing coolant, and of which a heat capacity is smaller than that of the engine body; a cooling device that is mounted in at least one of the plurality of coolant circulation paths and cools a flowing coolant; and a flow rate determination unit that determines a flow rate of a coolant allowed to flow through the exhaust system cooling unit based on a received heat amount that a coolant receives from an exhaust in the exhaust system cooling unit.
 3. The engine cooling device according to claim 1, further comprising: an estimation unit that estimates a temperature of a wall, which forms a flow path through which an exhaust gas flows, of the exhaust system cooling unit; and a correction unit that corrects a flow rate of a coolant determined by the flow rate determination unit based on the estimation.
 4. The engine cooling device according the claim 2, further comprising: an estimation unit that estimates a temperature of a wall, which forms a flow path through which an exhaust gas flows, of the exhaust system cooling unit; and a correction unit that corrects a flow rate of a coolant determined by the flow rate determination unit based on the estimation. 